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# Surds watch

1. Hi guys,

Was wondering if you could help me with the following surds questions...

Express:

(2sprt2 / sprt3 - 1) - (2sprt3 / sprt2 +1)

in the form psqrt6 + qsqrt3 + rsprt2, where the integers p. q and r are to be found.

I know you need to rationalise the denominator - but I never seem to get the right answers.

And the mark scheme misses out the step I am getting stuck on - the denominators I get correct after rationalising them looking at the mark schem of 2 and 1 respectively - but I cant get the numerator right - not sure how to simply the top when multiplying a single surd e.g. 2sprt 2 with sprt3 +1

Hope that makes sense....

Thanks!

Christina
2. (Original post by christinajane)
Hi guys,

Was wondering if you could help me with the following surds questions...

Express:

(2sprt2 / sprt3 - 1) - (2sprt3 / sprt2 +1)

in the form psqrt6 + qsqrt3 + rsprt2, where the integers p. q and r are to be found.

I know you need to rationalise the denominator - but I never seem to get the right answers.

And the mark scheme misses out the step I am getting stuck on - the denominators I get correct after rationalising them looking at the mark schem of 2 and 1 respectively - but I cant get the numerator right - not sure how to simply the top when multiplying a single surd e.g. 2sprt 2 with sprt3 +1

Hope that makes sense....

Thanks!

Christina
Like you know, you need to rationalise each one seperately, so - for example:

The numerator becomes .

Since .

You can do the same for the other fraction.
3. The question is incorrect. You can't express it in that form.
4. (Original post by morgan8002)
The question is incorrect. You can't express it in that form.
well I get p=-1, q=2, r=1

5. Presumably, Morgan is talking about the lack of brackets in the OP and hence the resulting ambiguity.
6. (Original post by Zacken)
Presumably, Morgan is talking about the lack of brackets in the OP and hence the resulting ambiguity.
Well that would just be pedantry. Although I wish more people would try a little Latex. Maybe I am just a Latex fetishist
7. (Original post by nerak99)
well I get p=-1, q=2, r=1

Yeah, assuming they made a few mistakes in typing up the question. What they wrote in the OP is insoluble.

(Original post by nerak99)
Well that would just be pedantry. Although I wish more people would try a little Latex. Maybe I am just a Latex fetishist

In maths you have to make your ideas clear and unambiguous. If you use notation incorrectly then someone will read something different to what you mean or it won't make sense. is pretty, but just using brackets where required is sufficient in most cases.
8. (Original post by morgan8002)
Yeah, assuming they made a few mistakes in typing up the question. What they wrote in the OP is insoluble.
In maths you have to make your ideas clear and unambiguous. If you use notation incorrectly then someone will read something different to what you mean or it won't make sense. is pretty, but just using brackets where required is sufficient in most cases.
Well in that case, where it is clear what the question was meant to be as opposed to what was written, it is a little obtuse to just state that the question was insoluble when what you mean is that the question "as stated" was insoluble. You could even try including the fact that you strongly suspect the OP was poorly typed.

That is, if you actually want " to make your ideas clear and unambiguous". Otherwise you risk looking a little smug.

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